The bandwidth of conventional VCOs is so narrow that multiband communications need a plurality of VCOs that take long settling time to attain the required frequency after power-on.
A spin-transfer torque oscillator (hereinafter, “spin oscillator”) which uses spin-transfer torque phenomena can be used for multiband communication apparatus by virtue of the frequency controllability by changing the amount of applied current of a single spin oscillator. Due to the short settling time of the spin oscillator, the spin oscillator can achieve high speed data transmission rate of 50 Mbps for FSK modulation or 500 Mbps for ASK modulation in the case of a single symbol modulation.
A spin oscillator can be integrated on a silicon substrate by the nanometer scale structure so that it has advantages of small size and mass production. However, so far, the spin oscillator cannot replace VCOs and is not to be used as a communication component because the output power of the spin oscillator is very low level of less than −40 dBm and its phase noise is high. The output power of less than −40 dBm limits the transmission distance and the required signal to noise ratio (SNR) cannot be achieved due to high phase noise characteristics.
Spin oscillators which are fabricated using nanoscale process show some problems of high fluctuation range of performance due to process variations and high fluctuation of the output power due to external force like magnetic field and the operational condition like the amount of applied current. Non-patent reference 1 discloses the simulation result which synchronizes two spin oscillators using a variable capacitor.